The present invention was prepublished by the inventor on March 28, 1985, on a poster at the Union of Suisse Societies of Experimental Biology (USSEB) meeting, Geneva, Switzerland, [cf. abstract in Experientia 41 (1985), 798].
Transcription enhancers are cis-acting DNA elements that are able to activate RNA polymerase II-transcribed genes in either orientation from a distance of up to several kbp from the promoter site (ref. 5,6), even when located downstream of the transcribed sequences (ref. 5; for reviews, see refs. 7-9). Originally detected in papovaviruses, their presence has since been demonstrated in a number of animal viruses, including herpesviruses such as herpes simplex (ref. 10), human cytomegalovirus (HCMV) (ref. 11), and Herpesvirus saimiri (ref. 12). Some enhancers, e.g. the enhancers from simian virus 40 (SV 40) and HCMV, can function in a number of different cell types, while others show a distinct host-cell preference. Enhancers that are associated with cellular genes, e.g. immunoglobulin genes (ref. 13-15), rat insulin (ref. 16), and a murine class II major histo-compatibility antigen gene (ref. 17), are often stricly cell-type specific.
It is envisaged that transcription enhancers can be used as important tools in genetic engineering experiments for the construction of expression systems for virus infectable eukaryotic cells. Such cells, especially vertebrate cells, transformed with a vector containing such enhancer and a structural gene would have higher transcription rates for messenger ribonucleic acids (mRNA) and hence can be expected to express more of the desired polypeptide encoded by the structural gene. As some of the known enhancers are not working in certain cells and the transcription rates are not necessarily high, there is a need for further enhancers able to fill this gap.